Melt flow rate (MFR) is inversely correlated to viscosity of the polymer. A high melt flow rate means that the polymer has a low viscosity and vice versa. While a few styrenic block copolymers have high melt flow rates, they achieve that with a high (>60 wt. %) diblock content and therefore have comparatively poor mechanical properties. The highest reported melt flow rate for any styrenic block copolymer, in the absence of additives to lower the viscosity and thus increase the melt flow rate, is 81 g/10 min. (As used herein including the claims, unless otherwise stated, “melt flow” shall mean the melt flow value determined according to ASTM D-1238, at 230° C. under a 2.16 kg mass.) This melt flow rate is disclosed in the following patent.
U.S. Pat. No. 7,439,301 to Handlin, Jr. relates to coupled block copolymers having high melt flow and high elasticity. The true molecular weight for the block copolymer is between 40,000 to 70,000; the polystyrene content (PSC) is between 13 to 25%, the vinyl content is between 60 to 85%, and a coupling efficiency of 89 to 97%.
U.S. Pat. No. 7,169,848 to Bening et al discloses selectively hydrogenated controlled distribution hS-B/S-S. The highest MFR in the examples is 17 g/10 min.
Historically, composite systems have been based on fiberglass mat plies or layers in addition to a binder. The binder could include non-reactive or reactive polymeric binder such as polyester, vinyl ester or epoxy resins, or a non-reactive resin such as asphalt or bitumen. The fiberglass mat plies are commonly used as structural support components for the composite. Composites are often designed to have maximum impact resistance while maintaining low density so that weight can be minimized. Traditional composite designs achieve toughness either through toughening of the reactive resin through the addition of dispersed rubber particles that arrest crack growth or through the use of optimized sizings on the glass fibers in order to improve adhesion between the glass fibers and the reactive resin binder. Both toughening mechanisms can also be used simultaneously. Materials that enable new composite designs or structures to enhance toughening performance or enable new composite designs or processing techniques, while maintaining low density, are industrially relevant and desirable. These resins have long lay-up times as well as long cure times. Due to the volatility of these resins, as well as the hazards of loose fiberglass strands, the manufacturing process of traditional composites suffers from adverse health, safety, and environmental problems. Boat hulls and decks, automotive body panels, and aerospace components are prime examples where these types of composites find utility. Large parts like boat hulls and decks are often constructed in outdoor locations, or in areas where there is only a roof overhead to allow the fumes to exhaust to the environment and lessen exposure to the workers.
Low viscosity coatings using styrenic block copolymers are virtually unknown because the copolymers normally have such high viscosity. Often a balance must be achieved between low volatile organic compounds (VOC), high solids content, and low viscosity. Obtaining a low viscosity coating based on hSBS and hS-B/S-S, so that the coating can be sprayed or roll applied onto a substrate, generally requires the use of higher amounts of organic solvents which adversely increase the VOC content and reduce the solids content. Therefore, styrenic block copolymers previously had limited applicability for low viscosity coatings where the VOC requirement is ≦350 g/L.
Styrenic block copolymers (SBC) have been employed in the adhesive market for hot melt, quick release covering, and pressure sensitive adhesives. Adhesives made with traditional hSBS (SEBS) are typically high cost with high performance while those made with traditional SBS are more suited for mid-cost, mid-performance markets. They are typically unsuitable for low cost adhesive markets or applications requiring low spray temperature of <325° F. Typically metallocene polyolefins or amorphous poly alpha olefins (APO) are utilized in low cost, low performance applications but result in lower adhesion strength and temperature resistance properties, which are important for certain hot melt adhesive applications. U.S. Pat. No. 7,348,376 to Gelles describes the combination of low melt flow rate hSBS polymers with APOs. However, these formulations lack the viscosity needed for application at low spray temperatures of <325° F.
The novel compound of the present invention is different than more conventional hSBS or controlled distribution hS-B/S-S because it has a very high melt flow rate, a corresponding low viscosity, and good tensile strength and elasticity. This also makes it possible for such polymers to participate in markets not typically considered, such as toughening fiberglass, low viscosity—low VOC polymer coatings, adhesives based on blended systems requiring low viscosity for improved processability, and film and non-woven personal hygiene applications. Thus there is a need for high melt flow rate hSBC products that have good performance characteristics such as strength and elasticity.